1. Field
The following description relates to a pixel and an organic light emitting display using the same.
2. Description of the Related Art
Recently, various flat panel displays (FPDs) having reduced weight and volume as compared to cathode ray tubes (CRTs) have been developed. The FPDs include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and organic light emitting displays.
Among the FPDs, the organic light emitting displays display images using organic light emitting diodes (OLEDs) that generate light through the re-combination of electrons and holes. The organic light emitting display has fast response times and is driven with low power consumption.
FIG. 1 is a circuit diagram illustrating a pixel of a conventional organic light emitting display. In FIG. 1, transistors included in the pixel are NMOS transistors.
Referring to FIG. 1, a pixel 4 of the conventional organic light emitting display includes an organic light emitting diode (OLED), and a pixel circuit 2 coupled to a data line Dm and a scan line Sn to control the OLED.
The anode electrode of the OLED is coupled to the pixel circuit 2 and the cathode electrode of the OLED is coupled to a second power source ELVSS. The OLED generates light with a predetermined brightness corresponding to current supplied from the pixel circuit 2.
The pixel circuit 2 controls an amount of current supplied to the OLED corresponding to a data signal supplied to the data line Dm when a scan signal is supplied to the scan line Sn. Therefore, the pixel circuit 2 includes a second transistor M2 (that is, a driving transistor) coupled between a first power source ELVDD and the OLED, a first transistor M1 coupled between the second transistor M2 and the data line Dm, and having a gate electrode coupled to the scan line Sn, and a storage capacitor Cst coupled between a gate electrode and a second electrode of the second transistor M2.
The gate electrode of the first transistor M1 is coupled to the scan line Sn, and the first electrode thereof is coupled to the data line Dm. The second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor Cst. Here, the first electrode of the first transistor M1 is one of a source electrode or a drain electrode, and the second electrode thereof is the other one of the source electrode or the drain electrode. For example, when the first electrode is a source electrode, the second electrode is a drain electrode. The first transistor M1 is turned on when a scan signal is supplied from the scan line Sn to supply a data signal supplied from the data line Dm to the storage capacitor Cst. At this time, the storage capacitor Cst charges a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor Cst, and the first electrode thereof is coupled to the first power source ELVDD. The second electrode of the second transistor M2 is coupled to the other terminal of the storage capacitor Cst and the anode electrode of the OLED. The second transistor M2 controls the amount of current supplied from the first power source ELVDD to the second power source ELVSS via the OLED corresponding to the voltage value stored in the storage capacitor Cst.
One terminal of the storage capacitor Cst is coupled to the gate electrode of the second transistor M2 and the other terminal of the storage capacitor Cst is coupled to the anode electrode of the OLED. The storage capacitor Cst charges the voltage corresponding to the data signal.
The conventional pixel 4 supplies a current corresponding to the voltage charged in the storage capacitor Cst to the OLED to display an image with a predetermined brightness. However, a conventional organic light emitting display using the above-described pixel cannot display an image having uniform brightness throughout the display due to deviations in the threshold voltages of the second transistors M2 in different pixels.
Specifically, when the threshold voltages of the second transistors M2 vary between different pixels 4, the pixels 4 generate light with different brightnesses corresponding to the same data signal, and an image with uniform brightness cannot be displayed or is very difficult to display.